Based on the basic equations of the nonlinear response of steel structures at the room temperature and high temperature

in which the effects of different factors

such as the geometric and material nonlinearity

the linear distribution of temperature along the longitudinal section are introduced

an computational program is developed and applied to investigate the nonlinear temperature response of one-story-two-span steel frame structures.The influence of the bending strain

the yielding-strength ratio

the stiffness ratio of beam to column and the initialize elastic module are analyzed

and the influence of the temperature step and the protection thickness on the fire resistance time of the structure is investigated too.The analysis results show that the bending strain

the yielding-strength ratio

the stiffness ratio of beam to column have evident effect on the middle deflection of beams and the top horizontal displacement of the side column

while have little effect on the top vertical displacement of the column.For these structures with the fire protection

the time step has little effect on the fire resistance time

while the effect of the protection thickness is evident.